The present invention relates generally to filters for injection molding machines and more particularly, to multi-stage axial flow filters for removing contaminants and particles from the melt prior to the injection of the melt into the mold.
It is desirable to provide injection molding machines with a means for filtering the melt and removing any contaminants from the melt prior to it passing through the injection molding machine nozzle into the mold. These contaminants are typically unmelted plastic granules, but can also include other materials such a metal bits and dirt which may become lodged in the mold cavities and interfere with the complete fill by the melt of the mold cavity.
One presently available filter is described in U.S. Pat. No. 4,434,053 and uses a cylindrical filter member which has a series of circumferentially-spaced axial grooves in its outer surface, which grooves include a series of fine radial holes radially extending from the grooves and communicating with an interior annular filter passage. Such a construction presents problems in that the radial holes can be easily clogged with contaminants and the melt will tend to accumulate in the radial holes upon cooling. When the melt has cooled, such a filter must be tediously cleaned with a pin or by the application of heat to open the holes. Additionally, the use of such small holes for filtration purposes increases the need to periodically remove the injection nozzle for filter cleaning purposes.
In a multi-stage injection molding filter incorporating the principles of the present invention, an elongate member includes a plurality of filter stages defined by sets of lands each having a different diameter which define a series of separate, axially aligned filter passages between the filter chamber inner wall and the filter member. A plurality of axial grooves are disposed in the filter member outer surface and are circumferentially spaced apart from each other. These grooves define melt inlet and outlet flow passages in the filter member. Additional axial grooves lie between and are disposed adjacent the inlet and outlet flow passages to define transfer passages which convey the melt from the first filter stage to the next filter stage.
Accordingly, it is a general object of the present invention to provide a new and improved axial flow multi-stage filter for injection molding.
It is another object of the present invention to provide an axial flow, multi-stage filter for use in injection molding machines which can be easily removed from the molding machine and cleaned.
It is another object of the present invention to provide an injection molding multi-stage axial flow filter having a first and second series of axial grooves which define respective inlet and outlet melt passages within the respective first and second filter stages and a third series of axial grooves peripherally spaced apart from the first and second axial grooves to define melt transfer passages extending between the first and second filter stages and communicating therewith.
It is yet a further object of the present invention to provide a cylindrical filter member having axially aligned multiple filter stages for use in an injection molding nozzle wherein each filter stage has a preselected filter clearance between the filter stag and the injection nozzle inner surface, and wherein the preselected filter clearance diminishes from a first filter stage filter clearance to a last filter stage filter clearance.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description taken in conjunction with the following drawings wherein like reference numerals indicate like parts.